{"id":35341,"date":"2022-08-11T00:00:00","date_gmt":"2022-08-11T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=35341"},"modified":"2022-09-12T11:13:23","modified_gmt":"2022-09-12T11:13:23","slug":"animating-jupiter","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/08\/11\/animating-jupiter\/","title":{"rendered":"Animating Jupiter"},"content":{"rendered":"\n

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Animating Jupiter<\/span><\/h2>\n\n\n\n

Transform your images of the gas giant into an awe-inspiring animation of its swirling storms and marvellous moons. <\/strong>
Pete Lawrence shows you how<\/strong><\/p>\n\n\n\n

\"\"
Follow our steps to make a captivating mini-movie of Jupiter and the motion of its moons <\/span><\/figcaption><\/figure>\n\n\n\n

As Jupiter begins to get higher in the sky as seen from the UK, its imaging potential continually improves. <\/p>\n\n\n\n

By photographing the planet with a high-frame-rate camera, it\u2019s possible to record the state of the gas giant\u2019s atmosphere. But you can also stitch together sequences of these images, creating animations showing how the planet rotates. These can be used to clarify atmospheric details as they turn with the planet, or reveal the orbital dance of the four bright Galilean moons. <\/p>\n\n\n\n

In this article we look at the techniques to make your own Jovian animations, from capture through to the final build. <\/p>\n\n\n\n

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The altitude of Jupiter is an important factor in how clear a view you\u2019ll get, with lower altitudes generally giving the worst view <\/span><\/figcaption><\/figure>\n\n\n\n

Capturing your images <\/span><\/strong><\/h4>\n\n\n\n

A little planning will ensure you capture the best images to animate <\/strong><\/p>\n\n\n\n

Jupiter is at its best when the atmosphere it\u2019s viewed through is stable. Atmospheric stability is affected by the weather, altitude of the object and the presence of the jetstream. You can determine when the most promising conditions are due from meteorological forecasts. Active fronts and deep low-pressure systems tend to cause instability, while high pressure tends to produce the most stable conditions. Weather dominated by high pressure with an absence of an overhead jetstream typically produces the best conditions, and websites such as Netweather provide jetstream forecasts for this: www.netweather.tv\/charts-and-data\/jetstream<\/a>. <\/strong><\/p>\n\n\n\n

It is when Jupiter is positioned due south that it\u2019s highest in the sky and above the thickest, most turbulent part of the atmosphere. If you work out how long you want to image for, you can time your session so the planet is due south at the mid-point. Jupiter moves a fair bit over a long session, so make sure it won\u2019t disappear behind any foreground objects. <\/p>\n\n\n\n

\u2018Still imaging\u2019 \u2013 taking a single frame of a target \u2013 tends to produce poor results with planets. A stills camera, such as a DSLR, captures a snapshot, frozen in time, which is typically heavily distorted by the atmosphere. \u2018Lucky imaging\u2019 is a better solution: taking many images in quick succession, harvesting the best and combining them into a single image. Often resulting in thousands of images, the results are analysed and organised by quality, aligned and averaged to reduce noise. Known as registrationstacking, this laborious process is largely automated by freeware programs such as RegiStax (www.astronomie.be\/registax<\/strong><\/a>) <\/strong>and AutoStakkert! (www.autostakkert.com<\/strong><\/a>). <\/strong>The final image these generate should be robust enough for post-capture tweaking. <\/p>\n\n\n\n

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Lucky imaging requires effort, but the results are often significantly better <\/span><\/figcaption><\/figure>\n\n\n\n
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Once one RGB set has been completed, each subsequent filtered capture can be used to complete a new full-colour image <\/span><\/figcaption><\/figure>\n\n\n\n

Low-altitude bright targets suffer from chromatic dispersion, creating colour fringes around their north and south edges. With a colour camera, an atmospheric dispersion corrector can reduce this, and a filtered mono camera can diminish the problem too. Capturing individual red (R), green (G) and blue (B) frames is an excellent way to get high-quality results. <\/p>\n\n\n\n

Taking multiple filter sequences means you have a choice of frames to combine. For example, by taking two RGB sequences you can create an image with the RGB from the first set, but also an image with R from the second set, and G and B from the first, and so on. An infrared-sensitive camera with an IR-pass filter will produce high-contrast results that will animate well, and wavelengths at the red end of the spectrum tend to be less affected by atmospheric instability. <\/p>\n<\/div><\/section>\n\n

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Dance of the moons<\/strong><\/h2>\n\n


The oscillating orbits of the Galilean moons make for an eye-catching video<\/strong><\/h4>\n\n
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Jupiter\u2019s four bright Galilean moons appear in a line, shining like stars near to the planet<\/figcaption><\/figure>\n\n

Jupiter\u2019s four largest, Galilean moons, Io, Europa, Ganymede and Callisto, are bright enough to be recorded with a conventional stills camera. With a large enough image scale, they can be shown clearly as separate entities to the planet and, over time, their movement around Jupiter can be recorded. <\/p>\n\n

There are several ways to accomplish this. One is to ignore the planet\u2019s disc entirely and simply adjust the exposure so the moons record as bright points of light. It pays to maintain a reasonably short exposure time here: too long an exposure can produce issues such as each moon \u2018dot\u2019 \u2018wiggling\u2019 at high frequency, due to instabilities in our atmosphere. If the telescope\u2019s mount isn\u2019t accurately polar-aligned, extended exposures will also result in the moons appearing as short lines rather than points. <\/p>\n\n

Lucky imaging can help overcome many of the vagaries introduced by our unstable atmosphere. If imaging simply to record a moon as a bright dot, you may still end up with a moon\u2019s image looking larger than it should, but it\u2019ll be tighter than it would be using a stills camera with a long exposure. <\/p>\n\n

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How long it takes each Galilean moon to travel the apparent diameter of Jupiter, based on their orbits when closest to Earth. For the positions of each moon throughout this month, see our chart in the Sky Guide in The Planets section <\/figcaption><\/figure>\n\n

The Galilean moons orbit Jupiter at different periods according to their distance from the planet. Innermost Io takes 1.8 Earth days, Europa 3.6 days, Ganymede 7.2 days and Callisto 16.7 days. Consequently, the fastest movement across the sky will be shown by Io. <\/p>\n\n

To create an animation sequence, determine how you want to image the moons: bright, or properly exposed. If you\u2019re just starting out, go for the bright option, adjusting your camera settings to record an over-exposed point of light. Then decide on the frequency of shots. If you\u2019re a novice, try to record a shot or frame sequence every 15 minutes, shortening the gap once you\u2019ve become more accustomed to building animations. For high-frame-rate captures, try to keep your individual capture lengths to no more than 60 seconds. <\/p>\n\n

You\u2019ll also need a point of reference for the final animation build, Jupiter being the obvious choice. If you intend to over-expose Jupiter, try to limit the over-exposure so you can still determine where the planet\u2019s edge is in each frame. This isn\u2019t an issue if you intend to capture the moon frames against a properly exposed planet. <\/p>\n\n

As you get more comfortable creating moon animations, you can adjust the period between captures, or change the image scale to create interesting compositions. <\/p>\n\n

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In this extreme close-up example, Jupiter\u2019s edge will be the reference point for the final animation. Typically, the whole of Jupiter would be in frame <\/figcaption><\/figure>\n\n

A planet in motion <\/strong><\/h4>\n\n

In video, the rapid spin and swirling air currents of Jupiter come dramatically to life <\/strong><\/p>\n\n

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With good seeing, there\u2019s amazing detail to capture in the gas giant\u2019s constantly changing atmosphere <\/figcaption><\/figure>\n\n

The banded atmosphere of Jupiter, full of everchanging detail, is an amazing sight to observe and image with a medium to large aperture reflector of 6 inches (150mm) upwards. Some features, such as the Great Red Spot, are large and obvious to see, while others may be subtle, appearing like small areas of noise on single still images. This is where animation really comes into its own. In an animated sequence, disc noise disappears between frames, while real features persist and rotate with the planet. <\/p>\n\n

There is some motion within Jupiter\u2019s atmosphere, but this is hard to see unless you\u2019re using special techniques. For example, with careful planning and luck with the weather, it should be possible to take an image of Jupiter at the same longitude over many rotations. Animating these will then reveal atmospheric features drifting and developing over time. <\/p>\n\n

Typically Jovian animations are done with frames recorded at regular intervals over an extended time of many minutes or hours. These sequence animations use the gas giant\u2019s limb as the anchor reference, the result showing how the features come and go as Jupiter rotates on its axis. With each rotation taking less than 10 hours, the results can be quite spectacular. <\/p>\n\n

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Transiting moons and their shadows make great animation subjects. Here Io shines bright through an infraredpass filter, the moon standing out against Jupiter\u2019s disc <\/figcaption><\/figure><\/div>\n\n
\"\"
By animating frames taken a specific number of rotations apart, you can reveal the movement of features such as cloud bands, spots and storms in Jupiter\u2019s atmosphere, and show how they change and evolve over time <\/figcaption><\/figure>\n\n

To capture images for an animation, a polar-aligned tracking equatorial mount is highly recommended. As well as keeping the planet in position on the camera sensor chip, this removes the need for post-capture orientation adjustment, as each image will have the same orientation. <\/p>\n\n

As was the case with the moon animation, carefully consider what the capture frequency should be. Bear in mind high-frame-rate captures typically require 30 to 60 seconds to record. A sequence of, for example, 50 seconds capturing the frames, then waiting 10 seconds, followed by another 50 seconds of capture and 10 seconds of waiting, will produce a very smooth animation but will also be labour-intensive. <\/p>\n\n

Longer intervals between captures take the pressure off, but the final animation won\u2019t be as smooth. Longer gaps also have the advantage of less data to handle and less post-capture processing to do. It\u2019s your choice, but we\u2019d recommend looking at a starting figure of 10 minutes between frames. <\/p>\n\n

The shadows cast by transiting moons make for particularly striking animations, providing good motion and image contrast with the steadily rotating Jovian globe. Moons involved in other events make excellent targets too. For example, consider animating a moon moving behind (occultation disappearance) or being revealed by (occultation reappearance) Jupiter\u2019s globe. Alternatively, a moon being hidden (eclipse disappearance) or revealed (eclipse reappearance) by Jupiter\u2019s shadow can make for a dramatic sight through larger apertures. <\/p>\n\n

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Building the animation<\/h2>\n\n

Free software and a little experimentation are all you need to create your animation <\/strong><\/p>\n\n

Step 1 <\/strong><\/p>\n\n

\"\"<\/figure><\/div>\n\n

Once you have a set of high-frame-rate capture sequences, it\u2019s recommended to make sure that their file names have the date and time within them. If not, consider prefixing them with the correct date and time in the format \u2018YYYYMMDD_hhmmss\u2019. Once ready, drag them into AutoStakkert! for processing.<\/span><\/p>\n\n

Step 2 <\/strong><\/p>\n\n

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You\u2019ll need to set the processing steps for the first image, and then subsequent images will be processed the same way. AutoStakkert!\u2019s interface may look a bit daunting, but the basic method of use is quite straightforward. Once you\u2019ve dragged in your frames, click \u2018Analyse\u2019 and let the program run.<\/span><\/p>\n\n

Step 3 <\/strong><\/p>\n\n

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Once done, under \u2018Stack options\u2019 set one of the \u2018Frame percentage to stack\u2019 values to 30. This means that 30 per cent of the input frames will be used. You can experiment with other values as you please. There are four settings that can be loaded and a further four for the specific number of frames to be used. <\/p>\n\n

Step 4 <\/strong><\/p>\n\n

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In the \u2018Frame View\u2019 window, select an appropriate alignment point size (try 48 if you\u2019re not sure), click \u2018Place AP grid\u2019, ensuring that the ensuing set of alignment point markers select only the planet. If not, you may have to adjust the \u2018Min bright\u2019 value and re-click \u2018Place AP grid\u2019. <\/p>\n\n

Step 5 <\/strong><\/p>\n\n

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Once done, press \u2018Stack\u2019 in the main program window. Let the program process all of the sequence files. If you choose to tweak the results, for example sharpening them using RegiStax, make sure you apply the same processes to each one. <\/p>\n\n

Step 6 <\/strong><\/p>\n\n

\"\"<\/figure><\/div>\n\n

Using the freeware PIPP application (sites.google.com\/site\/astropipp<\/a>), drag the still frames generated by AutoStakkert! into the main PIPP window. A dialogue will normally appear stating that \u2018Join mode\u2019 has been activated. Click \u2018Okay\u2019. <\/p>\n\n

Step 7 <\/strong><\/p>\n\n

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PIPP has many options that can be set and it\u2019s left to you to experiment with those not mentioned here. The base images are left untouched, and the worst it will do is fill up your hard drive, so feel free to experiment. <\/p>\n\n

Step 8 <\/strong><\/p>\n\n

\"\"<\/figure><\/div>\n\n

Select the \u2018Animation options\u2019 tab, then \u2018Play all frames in forward order\u2019. Under \u2018Output options\u2019, select the desired output format, eg animated GIF. Select the output folder. Select \u2018Loop frames repeatedly\u2019 and set an appropriate frame rate. If you get this wrong, just choose a different value and re-process. <\/p>\n\n

Step 9 <\/strong><\/p>\n\n

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Finally, select the \u2018Do processing\u2019 tab and click \u2018Start processing\u2019. Your output file will be created and stored in the selected output folder. It\u2019s that simple. If it\u2019s not right, adjust the appropriate setting within PIPP and re-process. By just tweaking the settings you can make a huge difference to your end result.<\/span><\/p>\n\n

Creating an animation of Jupiter isn\u2019t that much harder than generating a single image, it\u2019s just more processing-intensive, requiring steps that you\u2019ll need to repeat several times. Once you\u2019ve built your first animation, the results will hopefully encourage you to have another go. <\/p>\n\n

Don\u2019t be afraid to experiment, perhaps refining your technique to produce a smoother result. With Jupiter now climbing higher in UK skies and approaching its best appearance for the year, this is a great time to start producing your own Jovian movies. <\/p>\n\n

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Pete Lawrence is an expert astro-imager and a presenter on The Sky at Night<\/em><\/p>\n\n

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<\/p>\n\n

Pictures: PETE LAWRENCE<\/p>\n","protected":false},"excerpt":{"rendered":"

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